1. Field of the Invention
The present invention relates to a pattern inspecting method and an apparatus thereof, and a pattern inspecting method on a basis of an electron beam pictures or images and an apparatus thereof, with which a picture, displaying physical properties of an object such as a semiconductor wafer, TFT, a photo mask and so on, is obtained by use of an electron beam, a light or the like, and the obtained picture is compared with a picture which is obtained separately therefrom, thereby detecting defects or quasi-defects (or defective candidates), in particular the fine or minute ones thereof.
In a conventional art 1, as is described in Japanese Patent Laying-Open No. Sho 57-196377 (1982), there is already know a testing or an inspection, wherein a pattern including a repetitive pattern, being formed on an object to be tested or inspected such as a semiconductor wafer, is detected to be memorized, and the detected pattern is fitted or aligned with to a pattern which is memorized one time before, in an accuracy of degree of each pixel, thereby extracting a discrepancy or difference between the two patterns fitted or aligned with in the positions thereof so as to recognize or acknowledge the defects therein. Further, in a conventional art 2, as is disclosed in Japanese Patent Laying-Open No. Hei 3-177040 (1991), there is also known a technology, wherein a portion due to distortion or deformation in the detection points or positions between two pictures is improved among the problems of discrepancies or differences between the both images in normal portions thereof. Namely, in the conventional art 2, there is described the technology, wherein an object pattern is detected as a picture signal, and the detected pattern is aligned, or adjusted in the position by an unit of pixel with that which is memorized in advance or that which is detected separately. The two of them, which are aligned in positions by the unit of pixel (pixel unit), are further aligned in positions at a degree being finer or lower than the pixel (i.e., sub-pixel unit), so as to be compared and extracted errors therefrom in the image signals of those two patterns which are aligned in positions at the degree finer than the pixel, thereby recognizing or acknowledging the defect(s) of the pattern(s).
Between the two pictures to be compared, there exist the minute difference in the pattern shape, the differences in the values of gradation, distortion or deformation in the patterns, misalignment in positions and so on, even in a normal portion, due to a detection object sample itself and an image detection system thereof. Namely, as the discrepancies or inconsistency in the normal portion, there are some which are caused by the object itself and other(s) which are caused by a side of the testing or inspecting apparatus thereof.
The discrepancy or inconsistency caused by the test object is mainly due to a delicate difference caused through a wafer fabricating processes, such as etching and so on. This is because it looks to be the minute difference in shapes, or as the gray level difference between the repetitive patterns on the detected images.
The discrepancies, which are caused at the testing or inspecting apparatus side, include quantizing errors due to vibration of stages, various electric noises, mis- or mal- focusing and sampling, fluctuation in illumination light amount especially in a case of an optical system, fluctuation in electron beam current especially in a case of an electron beam system, and gaps or shifts in scanning position of the electron beam due to electrical charge of the sample and/or of an electronic-optical system, etc. In particular, in the electron beam system, influences due to geometric distortion is remarkable in the periphery portion of the test object. Those appear in the forms of differences in the gradation values of the portion of the image, the geometric distortion, and the gaps or shifts in the position.
In the conventional art 1 mentioned above, there are problems that, since the discrepancies occur even in the normal portion due to the causes of factors listed in the above, erroneous report occurs very often if each of those discrepancies is decided to be the defect restrictively or minutely, one by one. While, if a reference or criteria to decide the defect is loosen or lowered for preventing from the above, it is impossible to detect the minute or fine defect correctly.
Further, with the conventional art 2 mentioned above, though an only effect can be obtained in reducing or lowering the influence due to the misalignment in the positions between the pictures or images, among those influences due to the minute difference in the pattern shape, the differences in the gradation values, the distortion or deformation of the patterns, and the gaps or shifts in positions and so on, which are caused by the test object itself and the image detecting system thereof, but it is still not sufficient, nor takes the other problems into considerations thereof any more.
2. Summary of the Invention
An object is, according to the present invention for dissolving the problems of the conventional arts mentioned above, to provide a pattern testing method and an apparatus therefor, which can further reduce or lower the possibility of occurring the erroneous reports which are caused by the discrepancies or differences due to the sample itself and the image detecting system thereof, so as to enable the detection of the more minute or the finer defects.
Further, an another object of the present invention is to provide a pattern testing or inspecting method on a basis of electron beam picture or image and an apparatus thereof, which can further reduce or lower the possibility of occurring the erroneous reports which are caused by the discrepancies due to the sample and the image detecting system, on a basis of the electron beam picture of the test object itself, so as to enable the detection of the more minute or the finer defects.
Further, other object of the present invention is to provide a pattern testing method on a basis of electron beam picture or image and an apparatus thereof, which can further reduce or lower the possibility of occurring the erroneous reports which are caused by non-uniform distortion or deformation on the detected images due to the sample and the image detecting system thereof, on a basis of the electron beam picture of the sample, so as to enable the detection of the more minute or the finer defects.
Further, other object of the present invention is to provide a method and an apparatus therefor, having stable gradation values being suitable for testing, and being able to obtain an electron beam picture or image with less geographic distortion, in the pattern inspecting with use of the electron beam image of the sample.
Moreover, further other object of the present invention is to provide a method and an apparatus therefor, enabling the inspecting all over surface including a central portion and a peripheral portion as well, of the sample in the pattern inspecting with use of the electron beam image of the sample.
For dissolving the above objects, according to the present invention, there are provided a pattern inspecting method and an apparatus thereof and a pattern inspecting method on a basis of an electron beam image and an apparatus thereof, wherein inspection is made upon defect or defective candidate on a sample on the basis of a first data which are arranged in two-dimension, by making sampling values in physical quantity from a certain area selected on the sample as gradation values, and a second image data containing contents which can be a comparison sample for the first image data, and each of which has the following features.
Namely, according to the present invention, there are provided an image dividing and cutting-out step or means thereof, for memorizing said first image data and second image data sequentially for a predetermined area, and for dividing and cutting out each of those first and second data memorized sequentially into such a small area unit to be able to neglect such as the distortion therein; and a deciding step or means thereof, for comparing the first divided image and the second divided image, which are divided in the image dividing and cutting-out step or means thereof for the each division unit so as to calculate difference of the both images, and for deciding the defect or the defective candidate upon the basis of the difference between the both images, which are calculated for the each division unit.
Further, according to the present invention, there are also provided a position shift detecting step or means thereof, for detecting the position shift quantity between the first divided image and the second divided image, which are divided and cut out in said image dividing and cutting-out step or means thereof for the each division unit; and a deciding step or means thereof, for deciding to be the defect or the defective candidate by taking into considerations the position shift quantity which is detected in the position shift detecting step or means thereof, by comparing the first divided image and the second divided image, which are divided in the image dividing and cutting-out step or means thereof for the each division unit.
Further, according to the present invention, there are provided a position shift detecting step or means thereof, for detecting the position shift quantity between the first divided image and the second divided image, which are divided and cut out in said image dividing and cutting-out step or means thereof for the each division unit, and a deciding step or means thereof, for deciding to be the defect or the defective candidate, by comparing the first divided image and the second divided image, which are divided in the image dividing and cutting-out step or means thereof for the each division unit, so as to calculate the difference in the gradation values between the both images, and by basing upon a reference value for decision of containing fluctuating component in the gradation values which can be calculated out depending on the position shift quantity detected in the position shift detecting step or means thereof, with respect to the difference between the both images in the gradation values calculated for the each division unit.
Further, according to the present invention, there are provided a position shift detecting step or means thereof, for detecting the position shift quantity between the first divided image and the second divided image, which are divided and cut out in said image dividing and cutting-out step or means thereof for the each division unit; and a deciding step or means thereof, for deciding to be the defect or the defective candidate, by comparing the first divided image and the second divided image, which are divided in the image dividing and cutting-out step or means thereof for the each division unit, so as to calculate the difference between the both images depending upon the position shift quantity detected for the each division unit by the position shift detecting step or means thereof, and by basing upon the difference between the both images calculated for the each division unit.
Further, according to the present invention, there are provided a position shift detecting step or means thereof, for detecting the position shift quantity between the first divided image and the second divided image, which are divided and cut out in said image dividing and cutting-out step or means thereof for the each division unit; and a deciding step or means thereof, for deciding to be the defect or the defective candidate, by comparing the first divided image and the second divided image, which are divided in the image dividing and cutting-out step or means thereof for the each division unit, so as to treat the position shift compensation depending upon the position shift quantity detected for the each division unit by the position shift detecting step or means thereof, by calculating the difference between the first divided image and the second divided image on which the position shift compensation is treated, and basing upon the difference between the both images calculated for the each division unit.
Further, according to the present invention, there is also provided a step of means thereof, for compensating at least one of the gradation values so that the first divided image and the second divided image are nearly equal in the gradation values.
Further, according to the present invention, there is also prepared a compensation equation or a compensation data table for measuring the geographical distortion on the two-dimensional image having the electron beam image as the image contents thereof, and for compensating the distortion in advance, thereby controlling the electron beam scanning by using the compensation equation or the compensation data table.
Further, according to the present invention, there are provided a pattern inspecting method on a basis of an electron beam picture and an apparatus thereof, which are able to deal with the dynamic image distortion.
As mentioned in the above, according to the above constructions, in the inspection of patterns formed on the sample with use of the electron microscope, it is possible to reduce the possibility of bringing about erroneous or false reports due to the sample side and the inspecting apparatus side thereof, which are caused by discrepancies, such as the minute difference in pattern shapes, the difference in the gradation values, the distortion or deformation of the patterns, the position shifts, thereby enabling the detection of the defects or the defective candidates in more details. In particular, it is possible to deal with the dynamic image distortion.